Electronic devices may include imaging sensors capable of converting a light signal to an electronic signal that may be further processed for intended purposes such as display or storage. Imaging sensors may include a plurality of photosensitive elements arranged in an array including rows and columns. Each of the photosensitive elements may receive a portion of the light signal being received as a scene or as an image being sensed by the imaging sensor. Each of these portions of the image being sensed may be referred to as a pixel. The combination of these portions of the images captured as pixels by the array of imaging sensors represents the image being sensed by the imaging sensor. The portions of the image captured by each pixel may be represented by a electronic signal provided by a device such as a photodiode. In most instances, the electronic signal is further processed by one or more additional electronic circuits before the electronic signals may be used for one or more of its intended purposes.
In readout circuitry for complementary metal-oxide semiconductor (CMOS) imaging sensors, first-stage column amplifiers can be effective at reducing circuit noise. However, additional column-wise, fixed pattern noise at the output may result if the amplifier does not exhibit relatively high gain bandwidth and slew rate (to promote rapid settling of the output signal). In some applications, such as those using mega-pixel sensors, low current consumption is also desirable. Thus, there is a need for improved apparatus, methods, and systems that serve to reduce output noise and current consumption in CMOS imaging readout circuitry.